Hollingworthite is a rare platinum-group mineral typically occurring as microscopic inclusions within other platinum-group alloys or sulfide ores. Collectors rarely encounter it as hand specimens, as it is usually found via micro-analysis of ore samples from large igneous complexes.
Is this hollingworthite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch hollingworthite with a known reference. Hollingworthite sits at Mohs >6, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: grayish-black.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic.
- 4Match the color rangeCompare against the expected color range: gray.
- 5Look at form & habitCrystal system: cubic. Typical habit: anhedral grains, inclusions in platinum-group minerals.
Often confused with
Hollingworthite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Hollingworthite leaves grayish-black, Cobaltite leaves grayish black.
How to tell apart: Streak differs, so Hollingworthite leaves grayish-black, Gersdorffite leaves grayish black.
How to tell apart: Streak differs, so Hollingworthite leaves grayish-black, Sperrylite leaves black.
Often found alongside hollingworthite
Minerals reported to co-occur with hollingworthite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Rh(AsS)
- Mohs hardness
- >6
- Density
- 7.91 g/cm³
- Colors
- Streak
- Grayish-black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Cubic
- Crystal habit
- Anhedral grains, inclusions in platinum-group minerals
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector, Scientific study
- Host rock
- In platinum deposits in dunite pipes, layered ultramafic intrusives, and chromatites; in Cu–Ni sulfide ores
Where rockhounds find hollingworthite
Classic worldwide localities
- Upper and Banded zones of the Stillwater complex, Montana, USA
- Yuba River, Nevada Co., California, USA
- Goodnews Bay, Alaska, USA
- Merensky Reef, Bushveld complex, Transvaal, from the Driekop (type locality), Onverwacht, and Tweefontein mines, South Africa
- Sudbury and Werner Lake, Ontario, Canada
- Noril’sk region, western Siberia, and around Nizhni Tagil, Ural Mountains, Russia
Field-hunting tip
Where it forms: In platinum deposits in dunite pipes, layered ultramafic intrusives, and chromatites; in Cu–Ni sulfide ores. If you start seeing sperrylite, geversite, erlichmanite in float, you are in the right ground. Typical habit: anhedral grains, inclusions in platinum-group minerals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify hollingworthite?+
Where is hollingworthite found?+
Is hollingworthite safe to handle?+
What rocks look like hollingworthite?+
What minerals are found with hollingworthite?+
What kind of rock does hollingworthite form in?+
What is hollingworthite used for?+
Find hollingworthite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
